Recent global growth of wind projects has increased the need
for maintenance and repair work on turbine blades.1 As the market
expands, so too does the demand for greater blade spans. Companies are heading
this call by developing ever larger turbine technologies. The market must also
keep watch over aging turbine blades, which need to be looked after to ensure
they maintain performance and continue to provide the best return on
investment. Equally, a well repaired turbine blade can be as good as a new one,
if the repair remedies the damage and defects that have been hampering blade
performance.

A variety of environmental effects such as extreme
temperatures lead to the degradation of blades over their working lifetimes.
This degradation caused by erosion on the leading edge affects the drag and the
lift, and leads to reduction in aerodynamic efficiency and power production. Depending
on the drag increase and lift decrease, the loss of the annual energy
production of wind turbines can range from 2% to 25%.

Other issues that affect the functionality of the blades
include tip damage and trailing edge cracks, which all naturally arise over the
course of a turbine blade’s operational lifetime. As detrimental as these
challenges may be to the operation of the wind farm, these problems are not
insurmountable.

Repairs are performed to the internal structure of the
blade, the external surfaces of the blade, and to attachments of the blade.
This is all designed to make the blades more aerodynamic and increase annual
energy production of wind turbines. It is also essential to be cognisant of the
potential risks for the operations and maintenance (O&M) personnel to
perform repairs and sustain the functionality of the blades.

Internal repairs

These repairs typically demand some of the most intensive
work from technicians. Internal blade repairs include repairs to the bulkhead
brackets and sealing, and repairs to the inner laminations; or removing foreign
objects and retrofit solutions to optimise performance or minimise maintenance.
Repairs to laminations can require extensive preparation of the blade, cleaning
and ensuring a safe system for work within confined spaces, before the actual
work of repairing the inner laminate damage can begin. Internal damages can be
the result of sub-optimal manufacturing of, for instance, blade bulkheads.

Extensive damages such as lightning strikes can often mean
the turbine blade has to be removed from the nacelle and dropped to the ground
to be repaired, or replaced entirely. Internal repairs are often limited to
newer turbine blades and required to remedy known deficiencies early on in a
wind farm’s life.

External repairs

External repairs constitute the vast majority of repairs to
turbine rotor blades themselves. External repairs typically involve patching
and replacement of areas of the blade’s surface layers, which, as well as being
exposed to the elements, need to withstand the mechanical stresses placed upon
them as the blades flex and twist under loading. Rain erosion is recognised as
one of the major causes of turbine rotor blade damage, and early identification
and repair can prevent costlier repairs that could be required later on.2

Typical surface repairs can include simple scratches and
scrapes of the top coat that may require light patching, or damage to the
leading edge of the blade, or its protection, where it faces into the weather.
The largest portion of external damages are to the gelcoat, which will require
cleaning and sanding before the coat is applied, left to cure and then
smoothed.

Repairs of
aerodynamic add-ons

Blade attachments are designed to aid the aerodynamic
properties of the blade and boost performance. Aerodynamic additions to blades
are particularly important for ensuring that, as turbines age, owners continue
to realise optimal performance from their assets.

The wind industry continues to grow at a rapid pace, with an
additional 52GW of capacity installed in 2017, according to statistics
published by the World Wind Energy Association.3 Understanding the scope of
blade damage as it can occur on a wind farm is an important first step for
O&M teams to ensuring turbines are online and working as efficiently as
possible.

Global wind power
capacity

The overall capacity of all wind turbines installed
worldwide by the end of 2017 reached 539,291MW, according to preliminary
statistics published in 2018 by the World Wind Energy Association (WWEA). In
2017, the industry added 52,552MW, slightly more than in 2016 when 51,402MW
went online. This is the third largest number ever installed within one year,
after the record years 2015 and 2014. However, the association expressed
concern that the annual growth rate of only 10,8% is the lowest growth ever
since the industrial deployment of wind turbines started at the end of the 20th
century.

All wind turbines installed by the end of 2017 can cover
more than 5% of the global electricity demand. For many countries, wind power
has become a pillar in their strategies to phase out fossil and nuclear energy.
In 2017, Denmark set a new world record with 43% of its power coming from wind.
An increasing number of countries have reached a double-digit wind power share,
including Germany, Ireland, Portugal, Spain, Sweden and Uruguay.

China is by far the largest wind power market, and it installed an additional capacity of 19GW in 2017, slightly less than in 2016, The country continues its undisputed position as the world’s wind power leader, with a cumulated wind capacity of 188GW in 2018. Together with an amazing deployment in solar power, the country is now well on its way to making renewable energy its main energy source. ESI